Progressive failure analysis including stiffness reduction due to skin buckling and strength failure using closed form solutions

Kurzfassung

The usage of composite materials within modern aircrafts provides many advantages, such as weight reduction. During aircraft life the orthotropic material behaviour results in complex stress states within the composite. This challenges the sizing process of lightweight structures, which includes amongst others the analysis of the material strength and the buckling behaviour. To analyse the structural behaviour up to structural failure it is necessary to incorporate suitable calculation methods. State of the art progressive failure analyses (PFA) calculate damage propagation using the finite element method, which leads to high computational costs when optimizing large and high-resolution structures. This paper presents a progressive failure analysis, which predicts structure behaviour after buckling and strength failure using closed form solutions. Since the prediction after failure is not based on FEM, the presented PFA is less time consuming and is therefore more suitable within the optimization process of large structures, for example fuselage barrels. For strength failure initiation and the subsequent stiffness reduction several stress based failure criteria and degradation methods are implemented. Skin buckling is calculated by an analytical approach. For the stiffness reduction after skin buckling onset an additional reduction factor is derived from the load displacement curves of several nonlinear ABAQUS analyses that are used to calibrate the PFA.